According to some of the prior art methods of logical address assignment of HDMI (High-Definition Multimedia Interface), logical addresses are assigned via wired connections. The standard of HDMI is established in Non-Patent Document 1. According to HDMI, the logical addresses are used for identifying respective devices, thus transmitting control signals among the devices and enabling the devices to control each other (e.g., See Patent Document 1).
A logical address assignment method will be described which is used in the case that a plurality of devices conforming to HDMI standard are connected by wire using HDMI cables. Logical addresses represents 16 values ranging from 0 to F in hexadecimal, and each is associated with a type of a device. For example, when the device is a TV, it is represented by 0; when the device is a DVD player, it is represented by 4 or 8; and when the device is a Set Top Box (STB), it is represented by 3, 6, or 7.
At first, a physical address 0.0.0.0 is set in advance for a Sink device (e.g., a TV, projector, etc.). When the Sink device has a plurality of HDMI input ports, a physical address for a device to be connected to each input port is stored in a physical address carrying field of EDID (Extended Display Identification Data) which is provided in association with each port. The stored physical address is configured based on the physical address of the device itself, and a port number. For example, 1.0.0.0 is stored in a physical address carrying field of EDID associated with an input port with port number 1 of the Sink device, and 2.0.0.0 is stored in a physical address carrying field of EDID associated with an input port with port number 2. Once s Source device (e.g., a DVD player, STB, etc.) is connected to an input port of the Sink device, the Source device detects an HPD (Hot Plug Detect) signal indicating the connection. When the Source device detects the HPD signal, the Source device reads a physical address carrying field of EDID of the Sink device using DDC (Display Data Channel), and sets the read physical address as a physical address of the Source device itself. After setting the physical address, the Source device starts assigning a logical address to the Source device itself.
The Source device firstly selects one logical address from logical addresses associated with the type of the Source device itself. The Source device outputs a polling message destined for the selected logical address onto a CEC (Consumer Electronics Control) bus. Each device receiving the polling message returns an ACK when the destination logical address of the polling message is a logical address of the device itself. When any ACK for the polling message is not returned on the CEC bus, the Source device determines to use the selected logical address. On the other hand, when an ACK for the polling message is returned, the Source device determines that the destination logical address of the polling message has been already assigned to another device, and thus selects another logical address associated with the type of the Source device itself. The Source device outputs a polling message destined for the selected logical address onto the CEC bus, and when any ACK is not returned, the Source device determines to use the selected logical address. When an ACK is returned again, the Source device selects a different logical address and outputs a polling message in a similar manner.
Patent Document 1: Japanese Patent laid-open Publication No. 2004-208290.
Non-Patent Document 1: High-Definition Multimedia Interface Specification, Version 1.1, HDMI Licensing, LLC, California in U.S.A., May 20, 2004.